1. Field of the Invention
The present invention relates to a camera having a movable mirror for leading light emanated from an object to a viewfinder optical system, and in particular relates to a movable mirror drive mechanism and the structure of the peripheral part thereof in a camera. The present invention also relates to a control apparatus for a cam drive mechanism and a control method therefor.
2. Description of the Related Art
Inside SLR cameras, a movable mirror (quick-return mirror) is provided, which is capable of moving up and down; more specifically, capable of rotating between a mirror-down position (a position advanced into an optical path), in which the movable mirror is positioned in an optical path of an imaging optical system to reflect incident light emanated from an object (object-emanated light) toward a viewfinder optical system, and a mirror-up position (a position retracted from an optical path), in which the movable mirror is retracted from the optical path of the imaging optical system to allow the object-emanated light to travel toward a shutter. The shutter is provided behind the movable mirror and controls exposure on a photographic light-receiving medium such as an image sensor or silver-salt film, etc.
If the camera is structured such that the mirror drive mechanism for driving the movable mirror, and the shutter control mechanism for controlling the travel of shutter curtains (blades) and the charging operation of the shutter are separately arranged on the laterally opposite sides of the mirror box that accommodates the movable mirror, miniaturization of the camera in the lateral (widthwise) direction thereof is limited. By contrast, in the camera disclosed in Japanese Unexamined Patent Publication No. 2006-126389, the mirror drive mechanism and the shutter control mechanism are integrally arranged on one of the laterally opposite sides of the mirror box.
In addition, a drive mechanism which makes a cam member rotate using a motor and controls the operation of a driven object via a cam surface formed on the cam member has been widely used. For instance, in SLR cameras which incorporate a quick-return mirror, operations of the drive mechanism therefor are controlled such that the cam member is rotated by the driving force of the motor, which is a drive source of the drive mechanism, that a member having a cam follower (hereinafter referred to as the “driven member”) is moved via a cam surface of the cam member, and that the mirror-up operation, the mirror-down operation of the mirror drive mechanism and the shutter charging operation of the shutter charge mechanism are performed at predetermined timings.
The following cam members are known in the art as the type of cam member described above: an end-face cam rotatable about an axis of rotation which includes a cam surface formed at an end surface thereof in the direction along the axis of rotation, and a peripheral cam rotatable about an axis of rotation which includes a cam surface formed on a peripheral surface thereof surrounding the axis of rotation. In either of these cam members, the cam surface includes the following two cam areas: a cam area which presses the cam follower of the driven member in accordance with rotation of the cam member (specifically, an inclined cam area, the amount of projection thereof along the direction of the rotation axis increases in the direction of rotation of the cam member in the case of the end-face cam, or an inclined cam area the amount of projection of which away from the rotation axis increases in the direction of rotation of the cam member in the case of the peripheral cam), and a cam area which runs in the direction opposite to the direction in which the aforementioned cam area presses the cam follower as proceeding in the direction of rotation (specifically, an inclined cam area, the amount of projection thereof toward the axis of rotation decreases in the direction of rotation in the case of the end-face cam, or an inclined cam area which approaches the axis of rotation in the direction of rotation in the case of the peripheral cam). The former cam area and the latter cam area will be hereinafter referred to as the pressing cam area and the recessed cam area, respectively.
The cam follower is pressed under load conditions in the pressing cam area, whereas the direction of action of the load on the cam surface is reversed upon the area of the cam surface, against which the cam follower abuts, being switched from the pressing cam area to the recessed cam area. Variations of this load on the cam surface cause a difference in speed of rotation of the cam member during rotation thereof, so that there is a possibility of the rotational speed of the cam member with the recessed cam area in use becoming greater than assumed. Specifically, in the case where the driven member is biased in a direction to bring the cam follower into contact with the cam surface, the biasing force acts as an assisting torque in a direction to press the recessed cam area against the cam follower to promote (assist) rotation of the cam member, which enhances the tendency to increase the rotational speed of the cam member. Additionally, if the cam member rotates at high speed, the operating speed of the driven system including the driven member becomes greater than that in the case of using an assumed cam curve, so that there is a possibility of shock which acts on the driven system becoming great. For instance, in the mirror drive mechanism for SLR cameras, bouncing of the movable mirror upon completion of the mirror-up operation or the mirror-down operation becomes great, which limits an increase in photographing frame speed. Additionally, in the case where the rotational speed of the cam member is great and the angle of inclination of the recessed cam area of the cam surface (the amount of displacement given to the cam follower per unit of rotation angle of the cam member) is great, there is a possibility of the cam follower becoming incapable of following the cam surface and thus being instantaneously disengaged from the cam surface.
As countermeasures for the prevention of such malfunctions in the operation of the mirror drive mechanism in the recessed cam area, it is conceivable to reduce the inclination of the recessed cam area. However, if the inclination of the recessed cam area is reduced, problems with the cam member becoming great in size and with the cam curve deviating from an ideal cam curve arise. As another countermeasure for the preventing malfunctions, controlling the operation of the motor to apply a brake on the cam member to halt the cam member by driving the motor in the reverse direction or making the motor stop driving at a timing when no loads are imposed on the cam member and are known in the art (disclosed in Japanese Unexamined Patent Publication H05-69600).
In the case where the mirror drive mechanism and the shutter control mechanism are installed together on one of the laterally opposite sides of the mirror box, there is a problem with the space for installation of these mechanisms being limited due to mutual interference of the components thereof. Specifically, in the case where a motor for driving the movable mirror and a motor for charging the shutter are provided independently like the camera disclosed in Japanese Unexamined Patent Publication No. 2006-126389, it is difficult arrange the components in a limited space; for instance, instead of preventing the camera from increasing in size in the lateral (widthwise) direction, there has been a possibility of the camera increasing in size in the vertical direction (height direction) or the forward/rearward direction (optical axis direction). Accordingly, an objective of the present invention is to provide a camera capable of being made compact in size while having superior space utilization in the internal structure thereof.
In addition, if a brake is applied to the cam member via control of a motor upon the area of the cam surface in use (in operation) being switched from the pressing cam area to the recessed cam area, the rotational speed of the cam member becomes excessively small, which causes the operation of the driven system to delay with respect to an assumed timing. For instance, in the case where this motor control method is applied to the mirror drive mechanism for SLR cameras, the mirror-up operation and the mirror-down operation deteriorates in operating speed, which downgrades the performance in photographing frame speed. Accordingly, another objective of the present invention is to provide a control apparatus and a control method, for use to control a cam drive mechanism, each of which suppresses variations in the speed of the cam member due to load variations on the cam member and is superior in operating performance.
The first aspect of the present invention relates to a camera, including a movable mirror which is pivoted about a mirror up-and-down pivot orthogonal to an optical axis of an imaging optical system of the camera to be rotatable between an advanced position, in which the movable mirror is positioned in an optical path of the imaging optical system and is inclined at an angle to reflect incident light emanated from an object toward a viewfinder optical system of the camera, and a retracted position, in which the movable mirror is retracted upward from the optical path to allow the object-emanated light to travel toward a shutter which is installed in a rearward position with respect to the optical path; and a mirror drive mechanism for rotating the movable mirror. The mirror drive mechanism includes a slider which is supported on a side of the movable mirror to be linearly movable in a vertical direction that corresponds to an up-and-down rotation of the movable mirror, which rotates the movable mirror to the retracted position and the advanced position by moving upward and downward, respectively, the slider including a cam follower; an end-face cam member which is positioned above the mirror up-and-down pivot with respect to the vertical direction to be rotatable about a rotational shaft extending in the vertical direction, wherein the end-face cam member includes an end-face cam with which the cam follower is in contact, and the end-face cam member changes a position of the slider in the vertical direction via the end-face cam and the cam follower by rotating; and an end-face cam driver which rotates the end-face cam member.
“Upward/downward direction (vertical direction)” in the specification of the present invention denotes the direction of displacement of a predetermined point on the movable mirror (i.e., a direction substantially orthogonal to the mirror up-and-down pivot) when the movable mirror is rotated about the mirror up-and-down pivot as viewed from the front of the movable mirror (along the optical axis of the imaging optical system).
It is desirable for the end-face cam driver to include a mirror drive motor having a rotational output shaft, and a mirror-drive gear train which transmits a driving force of the rotational output shaft to the end-face cam member. The mirror drive motor is provided at a position away from the slider, in a camera widthwise direction along the mirror up-and-down pivot, with the rotational output shaft extending upward. The mirror-drive gear train includes a plurality of gears, each of which is rotatably supported by a rotational shaft extending in the vertical direction, the mirror-drive gear train being arranged in a space, defined in the camera widthwise direction, between the mirror drive motor and the slider.
It is desirable for the camera to include a shutter drive mechanism which is installed in the above-mentioned space.
It is advisable for the shutter charge mechanism, which is for making the shutter drive mechanism perform a shutter charge operation, to be configured of the following components. Namely, a charge lever which is pivoted about a charge-lever pivot which is parallel to the mirror up-and-down pivot and makes the shutter drive mechanism perform the shutter charge operation by swinging about the charge-lever pivot; a peripheral-cam-integrated member which is rotatably supported by a rotational shaft parallel to the mirror up-and-down pivot and makes the shutter charge lever swing in accordance with rotation of the peripheral-cam-integrated member; a shutter charge motor having a rotational output shaft parallel to the mirror up-and-down pivot; and a shutter-charge gear train which is configured of a plurality of gears, each rotatable about a rotational shaft parallel to the mirror up-and-down pivot and transmits a driving force of the rotational output shaft of the shutter charge motor to the peripheral-cam-integrated member. The shutter charge lever, the peripheral-cam-integrated member and the shutter-charge gear train are supported below the slider, and the shutter charge motor is supported below the shutter drive mechanism.
In addition, if the shutter charge lever, the peripheral-cam-integrated member and the shutter-charge gear train are configured to be supported below the slider and if the shutter charge motor is configured to be supported below the shutter drive mechanism, the arrangement of these components becomes superior, particularly in regard to space utilization.
It is desirable for the mirror drive mechanism, the shutter drive mechanism and the shutter charge mechanism to be arranged between a mirror box, which supports the movable mirror therein, and a battery chamber which accommodates a battery.
It is desirable for a camera body of the camera to include a front bulging portion which bulges forward from a front side of the battery chamber; a finger hooking recess which is formed between the front bulging portion and the mirror box; and a hand-held grip, a contour of which includes contours of the front bulging portion and the finger hooking recess, wherein the mirror drive motor is positioned behind the finger hooking recess.
It is desirable for the camera to further include an information display which is provided on top of the camera at an inclined position so that a front side of the information display is positioned higher than a rear side of the information display, with respect to a forward/rearward direction parallel to the optical axis. The mirror-drive gear train and the end-face cam member are at least partly arranged in a space formed below the front of the information display.
As an example of the specific structure of the slider, the slider can include a first slider which includes a first contact portion which contacts a pressed portion of the movable mirror holding member from below, wherein the first slider presses the pressed portion at the first contact portion to thereby rotate the movable mirror to the retracted position when moving upward; a second slider, which is movable relative to the first slider in the vertical direction, which includes a second contact portion which contacts the pressed portion of the movable mirror holding member from above, and wherein the second slider presses the pressed portion at the second contact portion to thereby rotate the movable mirror to the advanced position when moving downward; and a resilient connecting member which biases the first slider relative to the second slider in a direction to reduce a distance between the first contact portion and the second contact portion.
In this case, it is desirable for the cam follower to be provided on the first slider, wherein the camera further includes a slider biaser which biases the first slider upward to make the cam follower come into contact with the end-face cam. The resilient connecting member biases the second slider downward toward the first slider with a biasing force greater in biasing force than the slider biaser.
It is desirable for the first slider and the second slider to include a clearance limit portion which limits a minimum clearance in the vertical direction between the first contact portion and the second contact portion. A size of the minimum clearance, which is defined by the clearance limit portion, is determined to allow the pressed portion of the movable-mirror holding member to be held between the first contact portion and the second contact portion with a predetermined clearance therebetween.
The second aspect of the present invention relates to a control apparatus and a control method for a cam drive mechanism.
In an embodiment, a control apparatus for a cam drive mechanism is provided, including a motor; a driven member having a cam follower; a rotatable cam member which rotates by a driving force of the motor; a cam surface which is formed on the rotatable cam member, the cam surface including a pressing cam area which is inclined so as to press the cam follower against a load when the rotatable cam member is rotated by rotation of the motor in a single direction, and a recessed cam area which is inclined in an inclination direction opposite to an inclination direction of the pressing cam area; and a motor controller which rotates the rotatable cam member by the rotation of the motor in the single direction. The motor controller changes a rotational speed of the motor between a time when the rotatable cam member is positioned at a first rotational position thereof at which the recessed cam area and the cam follower are faced against each other, and a time when the rotatable cam member is positioned at a second rotational position thereof at which the pressing cam area and the cam follower are faced against each other.
In an embodiment, a method is provided for controlling a cam drive mechanism, including a motor, a driven member having a cam follower, a rotatable cam member which rotates by a driving force of the motor, and a cam surface which is formed on the rotatable cam member and includes a pressing cam area which is inclined so as to press the cam follower against a load when the rotatable cam member is rotated by rotation of the motor in a single direction, and a recessed cam area which is inclined in an inclination direction opposite to an inclination direction of the pressing cam area, wherein the method includes rotating the motor in the single direction at a predetermined speed when the rotatable cam member is positioned at a first rotational position thereof at which the pressing cam area and the cam follower are faced against each other, and rotating the motor in the single direction at a speed that is different from the predetermined speed when the rotatable cam member is positioned at a second rotational position thereof at which the recessed cam area and the cam follower are faced against each other.
In either of the control method or apparatus, when the rotatable cam member is positioned at the first rotational position, it is desirable for the motor controller to control an operation of the motor so that the motor rotates the rotatable cam member at a speed that is slower than that when the rotatable cam member is positioned at the second rotational position.
The rotational speed of the motor can be changed by changing the duty ratio of a pulse waveform for driving the motor or by changing the motor drive voltage.
It is desirable for the motor controller to change the duty ratio by making an energizing period and a non-energizing period of the motor in a cycle period different in duration from each other. Alternatively, it is desirable for the motor controller to change the duty ratio by setting a duration of a short-circuit in a cycle period between terminals of the motor.
The duty ratio when the rotatable cam member is positioned at the first rotational position, at which the recessed cam area and the cam follower are faced against each other, is preferably smaller than 50 percent.
The second aspect of the present invention is effective especially in a configuration in which the biasing force in a direction to bring the cam follower into contact with the cam surface acts on the driven member.
It is desirable for the control apparatus to include a biaser which exerts a biasing force on the driven member in a direction to bring the cam follower into contact with the cam surface, wherein the load acts on a rotation of the rotatable cam member due to the biasing force on the driven member when the pressing cam area of the cam surface presses the cam follower, and a torque in a direction to assist rotation of the rotatable cam member acts on the rotatable cam member due to the biasing force on the driven member when the cam follower comes into contact with the recessed cam area of the cam surface.
Namely, variations of the load on the rotatable cam member become great due to the biasing force on the driven member; however, variations in rotational speed of the rotatable cam member can be suppressed by control of the rotational speed of the motor according to the present invention.
It is desirable for the control apparatus to include a code plate mounted on the rotatable cam member, and a contact brush having a terminal which selectively contacts lands on the code plate. The motor controller detects a rotational position of the rotatable cam member from changes in relative contact position between the contact brush and the lands to control the rotational speed of the motor.
According to the first aspect of the present invention, an internal structure including the drive mechanism for the movable mirror is efficiently arranged in a space alongside one side of the movable mirror, which makes it possible to achieve a compact camera even though it is configured of a relatively large number of components.
According to the control apparatus and the control method for the cam drive mechanism of the second aspect of the present invention, by varying the rotational speed of the motor in accordance with load variations on the rotatable cam member, variations in the speed of the rotatable cam member due to the load variations can be suppressed, which makes it possible to drive the rotatable cam member according to an assumed cam curve. Specifically, by driving the motor at a reduced speed, rather than driving the motor in the reverse direction or making the motor stop driving, in a state where the recessed cam area and the cam follower face each other, the rotatable cam member can be prevented from being accelerated, and the rotational speed of the rotatable cam member can be prevented from being excessively reduced, which makes it possible to give excellent operating performance to the cam drive mechanism.
The present disclosure relates to subject matter contained in Japanese Patent Application Nos. 2013-157532 (filed on Jul. 30, 2013) and 2013-201697 (filed on Sep. 27, 2013) which are expressly incorporated herein by reference in their entireties.